Various types of diagnostic tests have been conducted to diagnose defective portions of each device built in the computer apparatus. For example, Japanese Laid-open Patent Publication No. H06-4413 discloses a memory-diagnostic test that diagnoses whether the memory-function of each of built-in memories correctly functions (for example, whether predetermined data can be properly read from or written to memory).
In this type of computer apparatus, a diagnostic program corresponding to each device is stored in part of an internal read only memory (ROM). After an operation system (OS) is started up, a processor such as a central processing unit (CPU) loads the diagnostic program into a main memory such as a random access memory (RAM) and executes it to conduct various diagnostic tests.
However, in the conventional computer apparatus described above, when there is an abnormality in the processor, the diagnostic tests cannot be properly conducted. Specifically, the processor performs a plurality of functions, and accordingly, if there is a defective function which cannot be performed in the functions, the operation of the processor becomes unstable. Therefore, the diagnostic programs cannot be properly executed.